1. Field of the Invention
The present invention relates to a structure for preventing current from leaking out of devices such as a valve, an intermediate reservoir, etc., which are employed in an electrostatic spray coating apparatus for applying a desired voltage to electrically conductive paint so as to electrostatically spray-coat a workpiece therewith.
2. Description of the Related Art
As an electrostatic spray coating or painting apparatus for applying a high voltage to electrically conductive paint so as to electrostatically spray-coat an object such as a car body to be coated therewith, there has heretofore been known a paint color-changeover system disclosed in Japanese Patent Application Laid-Open No. 2-2885, for example.
According to the disclosure, the paint is first introduced into an intermediate reservoir electrically insulated from ground potential. Thereafter, the paint is supplied via a paint passage from the intermediate reservoir to a spray gun subjected to a high potential. Thus, a process for electrostatically spray-coating the object to be coated with the paint is carried out.
In the above disclosure, even the intermediate reservoir has been subjected to a considerable high voltage. It is therefore necessary to make devices such as the intermediate reservoir, various valves of insulating materials. However, the devices made of the insulating materials has problems in accuracy and strength, and the manufacturing cost is raised.
Further, a line is coupled to the devices through a joint. Thus, current tends to leak from the joint. When an electric conductor such as a human body approaches one of the devices, an electric discharge takes place due to insulation breakdown.
Therefore, there has been made the following approach. For example, a block valve mechanism disposed between a paint feed source and an intermediate reservoir, the intermediate reservoir, and a flow control valve for controlling the delivery rate of electrically conductive paint supplied to a spray gun from the intermediate reservoir are spaced away from one another by a distance required to reliably provide insulation against a high voltage applied to the paint. Under this condition, they are disposed on the same plane.
In the disclosure referred to above, however, the devices such as the block valve mechanism, the intermediate reservoir and the flow control valve are spaced away from one another by the distance referred to above. Therefore, spaces for disposing the devices are greatly increased. Further, since the devices are exposed to the outside, there is much risk of an electrical short when a robot arm approaches the devices, for example.
As a result, the devices cannot be disposed within a spray booth or near an electric conductor. In addition, the length of the line extending up to the spray gun increases. Therefore, paint is wasted in quantity when a color changeover process is performed. Further, much cleaning time is required and the quantity of cleaning liquid to be used is increased.